Radial roller bearings are bearings that support mainly a load applied to a rotating shaft in the radial direction (diameter direction) and include an outer ring member and a plurality of roller members (rollers) that roll on the inner surface thereof. Such radial roller bearings often further include a cage-shaped retainer (retainer) that keeps the individual roller members equally spaced. Among others, radial roller bearings including roller members having an L/D of far more than 1, where D is the diameter of the roller members and L is the length of the roller members, and an outer diameter of the roller members far smaller than the diameter of the shaft to be supported are called radial needle bearings. Examples of known rotary machines equipped with such radial needle bearings include compressors for compressing a refrigerant in a car air conditioner (see, for example, PTL 1).
Rotary machines that constitute comfort equipment, such as compressors as described above, are required to generate a minimum level of noise during operation. In the related art, PTL 2 discloses a technique in which each roller member of a thrust needle bearing, which supports a load on a rotating shaft in the thrust direction, is tapered from the rolling surface toward at least one end surface thereof to form a crown portion such that the circularity of the rolling surface in a cross section taken in the diameter direction is a predetermined level or less and that the rolling surface includes a straight portion parallel to the axis of the roller member in a cross section taken in the axial direction, thus stabilizing the rolling motion of the roller members and thereby reducing the noise therefrom.